1. Field of the Invention
The field of the invention relates to assemblies for feeding envelopes or sheets to the printing drums or rollers of a printing press, and particularly to pusher block assemblies for urging the envelopes or sheets towards the drums or rollers.
2. Brief Description of the Prior Art
Assemblies referred to as aligners are employed in printing presses for feeding envelopes and other sheet-like items to printing stations. Aligners are often comprised of a pair of parallel, endless chains to which pusher block assemblies are affixed. The pusher block assemblies include rod-like elements known as pushers. The pushers engage the rear edges of the envelopes, ensuring that the envelopes are fed to the print rollers in proper orientations for printing. U.S. Pat. Nos. 4,588,184 and 4,717,142 disclose aligners known to the art.
A printing press is ordinarily used to print many different sizes of items. In order to print relatively long items exceeding the spacing along the chain between successive pushers, it may be necessary to remove a number of pusher block assemblies from the aligner chains in order to prevent them from contacting the bottom surfaces of the items. Such contact can result in misalignment and/or jams as the items are fed to the printing rolls. The pusher block assemblies are reattached to the aligner chains when shorter items are to be printed in order to maximize the efficiency of the press. The removal and reattachment of pusher block assemblies can be a time-consuming process, requiring precise alignment and resulting in delays before the press can again be used in an efficient and effective manner. U.S. Pat. No. 5,165,523 discloses the removal of pusher block assemblies for accommodating large size envelopes.
In feeding items such as envelopes to the print rollers, it is also important to avoid damaging the trailing edges of the items, which are engaged by the pushers until they exit the aligner section of the printing press. Such exiting occurs as the chains move about a sprocket, thereby causing the pushers to travel about an arc. If the pushers cause a downward force to be exerted upon the trailing edges of the items as they exit the aligner section, these edges can become creased or otherwise damaged. U.S. Pat. No. 4,986,522 discloses a pusher block assembly including means for preventing envelopes from being hung up by the pushers.